During the irradiation treatment of fluids flowing through fluid passageways, the uniformity of irradiation is of primary importance. By way of example, the fluid might be treated with ultraviolet irradiation so as to disinfect, purify, or cause oxidation of material within the fluid. If the irradiation is not uniform, those portions of the fluid flowing through the regions of low irradiation intensity may be undertreated, while portions in the vicinity of peak irradiation fields may receive higher than desired doses of irradiation which could damage material within the fluid. This problem is even more significant in the case of turbid fluids or fluids of high absorptivity for the applied irradiation.
Known techniques for irradiation of volumes of fluid include immersing multiple irradiation sources in the fluid. However, this is complex and costly, requiring multiple irradiation sources and introducing additional problems of cumulative absorption caused by impurities on the irradiation source-fluid interface. Cleaning mechanisms and processes have been proposed to overcome this last problem, but these are likewise elaborate and complex. Potential irradiation source accidents introduce additional risks of pollution of the fluid and the distribution system by the hazardous irradiation source components.
A second approach is to restrict the fluid flow, avoiding underexposed volumes. This scheme suffers from limited efficiency, high pressure drops, and high cost of pumps necessary to achieve the desired flow.
Another approach is to introduce mixing devices in the fluid flow, in the hope that each portion of the fluid will receive an “average” treatment. This approach likewise suffers from efficiency problems, as well as the more serious problems of likely undertreatment of a portion of the fluid volume.
A further approach is to present the fluid as a thin film to the irradiation. This approach does not take into account the absorption of the source, the fluid passageway, and the fluid itself, nor the indices of refraction of the fluid passageway material or the fluid, and hence the real energy distribution in the thin film of fluid.